How robust are pollination networks?: an assessment using alpine pollination and simulated networks

Abstract

[eng] High robustness of complex ecological systems in the face of speciesextinction has been hypothesized on the redundancy in species. We explored howdifferences in network topology may affect robustness. We created synthetic net-works to study the influence of the properties of asymmetry of network dimensions,connectance and type of degree distribution on network robustness. In syntheticand pollination networks, we used two extinction strategies: node extinction andlink extinction, and we simulated three extinction scenarios differing in the order ofspecies removal (least-to-most connected, random, most-to-least connected), toevaluate the robustness of 10 alpine pollination networks. In addition, we assessedrobustness to extinction of simulated networks, which differed in one of the threetopological features. Our study indicated that robustness of alpine pollinationnetworks is dependent on the topology of each network. Simulated networks indi-cated that robustness increases when (a) extinction involved those nodes belongingto the most species-rich trophic level and (b) networks had higher connectance.We also compared simulated networks with different degree-distribution networks,and they showed important differences in robustness depending on the extinctionscenario. In the link extinction strategy, the robustness of synthetic networkswas clearly determined by the asymmetry in the network dimensions, while thevariation in connectance produced negligible differences.